Transmission problem

[tinindian95]

I have an odd problem with the transmission in my 95 GTP that I have not been able to figure out. When I first start up the car and drive it for a while it runs fine and shifts through all of the gears normally with no problem. Once the car is up to temp and I'm driving on the highway the car will shift out of overdrive and into 3rd gear and will not go back into overdrive unless I turn the car off and restart it again. If I don't restart the car it will only upshift as far as 3rd gear even if I am stopped at a light and then go again when it turns green. I have turned it off and restarted it while on the fly at 60mph and then it will go back into overdrive again. I'm stumped, anybody have or had this problem with there's? Any help would be greatly appreciated, thanks.

[bszopi]

Have you checked fluid levels lately? This happened to me a few times several years ago, but never figured out why. Someone else has mentioned this semi-recently, though... Might look through some posts for the last 5-6 months for people loosing overdrive (or 4th gear).

[tinindian95]

Yeah, the fluid level is good, someone told me it might be a problem with the computer?

[3400-95-Modified]

My 96 would do that but it would also throw a code of trans component slip... And that was when I had a different geared transmission in my car so the RPM's didn't match up to the MPH that it wanted to see. Did you swap in a different trans at anytime? Might also just be slipping in 4th or tcc lock and its just dropping it out to prevent damage.

[Azrael]

I had a similar issue but it was just low on fluid due to a leaky fluid cooler pipe. Is the engine idling and everything fully warmed up when you check the fluid level? It will read higher than it really is when the engine's off.

[tinindian95]

The fluid level in the car is fine. I know what I'm doing as far as that goes, I've been around cars most of my life. I'm just not that knowledgeable when it comes to computerized cars. I'm thinking it's something electronic or computer controlled because if I turn the car off and re-start it it is fine again sometimes for days at a time. It is very intermittent, which makes me think it's electronic. If it was consistent it would lead me to believe it be more of a mechanical issue.

[robertisaar]

you know what? i think either your trans temp sensor is bad, or your trans is heating up that much to where the PCM goes into failsafe mode.

[tinindian95]

If it was running hot and went into a failsafe mode, why would it downshift it into 3rd so that it would rev even higher? I would think that would make it run even hotter, right?

[robertisaar]

not quite sure what GM was thinking with that one, but it does happen.

here's a description that sounds like what is happening. try and find someone with a scanner or laptop/aldl cable and see what the trans temp sensor is saying when this happens.

[tinindian95]

Interesting, thanks I'll check it out.

[pocket-rocket]

Turning faster would pump more fluid through the cooler. That's the only thing I can think of why they do it. It's kind of contradicting though considering my car would never go into OD or lock the TCC until it had warmed up. Even my wife's car waits until it's up to the first mark on the gauge.

[robertisaar]

maybe it's GM's way of saying "hey dumbass, your tranny is overheated, that's why i'm not letting you into 4th, maybe you should stop?"

at least the waiting to engage 4th/TCC makes sense.

[pocket-rocket]

That's an awful subtle approach. I mean, most people I know would just push the gas harder to keep at speed.